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Trouble with Hartke 3500 Head

Discussion in 'Amps and Cabs [BG]' started by blowfly, Sep 27, 2008.

  1. I just bought an old, beat up Hartke 3500. These have the dual pre-amp where you can blend the solid state pre-amp with a tube pre-amp to get the tone you want. The tube channel is completely dead, even after replacing the old tube with a fresh JJ/Tesla 12AX7. :crying: The solid state sounds so good that I still can use the amp, and I was able to buy it for chump change so it's not a complete disaster. Still, I wonder if there might be a cheap and easy fix to get the tube side working. I am on a tight budget right now and I don't know of a good repair shop in my area (Riverside-San Bernardino, So.Cal.) I would really appreciate any helpful advice. Thanks!!
  2. craig.p


    Sep 28, 2008
    New Hampshire
    If I were working on it, I'd first check to see whether *both* heaters are lit up orange. If not, then there's something wrong with the filament voltage source. You will need a simple voltmeter. Expect to see 6 or 12 volts

    If the above was ok, I'd check to see whether both plates had high voltage on them. The plate voltage source might have died. Watch out -- we're talking a couple hundred volts here and it WILL knock you right into next week if you're not careful.

    With filaments lit and plates having the proper voltage, the next step is to inject a signal at the amp input and (groan) trace it down the line. Not much fun, but sometimes you've just gotta go there. :-\

    I suppose it's possible the amp was dropped and something came loose, or a wire came undone, or an etch on a circuit board cracked, or there's a cold solder joint that let go. Are the tube sockets chassis-mounted or soldered directly to a circuit board? I don't know, but you can check. Get in there and have a look around with a magnifying glass and a STRONG light source so you can see all the fine details.

    Also, sometimes tube sockets loosen up with age. If the amp was on the road, that could be your problem. Tighten up all 9 tiny pin sockets which are part of the tube socket.

    Another thought: it's possible the tube section started humming like mad (for whatever reason) and someone went in and disabled it, i.e. clipped a wire or two in the audio chain, rather than try to locate the root cause.

    Tough to tell w/o seeing in in person. Either way, though, you're going to have to open it up.
  3. Thanks for the advice. I am going to get a friend that knows a lot more than I do about electronics to help me check out the things that you suggested. I am sure your ideas will be a big help! :)

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